Current collector, negative electrode and battery

ABSTRACT

A current collector including a first principal plane and a second principal plane. In the current collector, the roughness of the first principal plane and second principal plane being mutually different.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/687,848 filed Mar. 19, 2007, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentinvention contains subject matter related to Japanese Patent ApplicationJP 2006-095608 filed in the Japanese Patent Office on Mar. 20, 2006, theentire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery including a positiveelectrode, a negative electrode, an electrolyte, and a negativeelectrode current collector, at least part of which is formed as a roughsurface, and also relates to a current collector and a negativeelectrode forming the battery.

2. Description of the Related Art

With progress in science and technology such as semiconductortechnology, personal computers (PCs), mobile phones, and the like havebeen developed, and batteries utilized as power supply for electronicapparatus have been expected to facilitate handling of the batteriessuch as reduction in size and weight, and to exhibit excellent electricproperties.

In view of such expectations, the following types of lithium-ionsecondary batteries have been developed and have widely been used: alithium-ion secondary battery having a graphite material that uses anintercalation reaction of lithium (Li) between graphite layers, or alithium-ion secondary battery utilizing a carbonaceous material as anegative electrode active material to which lithium insertion andextraction into pores are applied.

In recent years, as increasing in power and time consumed for theelectronic apparatus due to higher performance of the electronicapparatus, an increase in capacity and power generation of a secondarybattery have been desired, and especially in capacity, propertyimprovement has much been desired.

A battery including a negative electrode active material layer formed ofa carbon material such as graphite may be difficult to greatly improveproperties because a battery capacity of the negative electrode activematerial is about to reach the theoretical limit.

Increasing a thickness of an active material layer may improve batterycapacity; however, if such thick electrode is formed of a smooth currentcollector typically used in the related art, peeling (detaching}strength decreases to deteriorate cycle characteristics of the battery.Further, if an amount of a binder is increased so as to control to lowerpeeling strength, load characteristic of the battery is lowered, therebyadversely affecting the cycle characteristics of the battery.

Japanese Unexamined Patent Publication No. 2003-7305 and JapaneseUnexamined Patent Publication No. 2004-95474 disclose a method offabricating a battery using a thin plate-form current collector thatincludes rough surfaces of both principal planes to control to lowerpeeling strength. Such a current collector having rough surfaces mayimprove peel strength without extremely increasing amount of the binderas described above. However, if such a current collector includes roughsurfaces for lowering peeling strength, the current collector may becomesusceptible to crack or fracture.

While, a negative electrode active material containing silicon (Si), tin(Sn), metal lithium (Li), and the like has been examined. Since such anegative electrode active material can be inserted much lithium (Li) ascompared a case with a carbon material, capacity of the battery maygreatly be increased.

However, since the negative electrode active material containing silicon(Si) and tin (Sn) drastically changes its volume when charging anddischarging the battery, the inner pressure increases to impose loadsupon members located around the negative electrode active material.Further, in an electrode having an alloyed interface between a currentcollector and an active material layer, both the current collector andthe active material layer may be cracked or fractured, resulting inlowering the battery capacity.

SUMMARY OF THE INVENTION

In view of the aforementioned aspects, according to an embodiment of thepresent invention, there are provided a battery including a negativeelectrode formed of a current collector, part of which includes roughsurface, and in which occurrence of crack or fracture are controlled, acurrent collector and a negative electrode that may form the battery.

According to an embodiment of the present invention, there is provided acurrent collector including a first principal plane and a secondprincipal plane, with roughness of the first principal plane and thesecond principal plane being mutually different.

According to an embodiment of the present invention, there is alsoprovided a negative electrode, including a current collector having afirst principal plane and a second principal plane, with roughness ofthe first principal plane and the second principal plane being mutuallydifferent.

Further, according to an embodiment of the present invention, there isprovided a battery having a positive electrode, a negative electrode,and an electrolyte that includes a current collector having a firstprincipal plane and a second principal plane, with roughness of thefirst principal plane and the second principal plane being mutuallydifferent.

According to an embodiment of the present invention, in the batteryformed of the current collector and the negative electrode, occurrenceof crack or fracture on the negative electrode may be controlled, andespecially if the negative electrode active material layer is formed ofthe negative electrode active material that drastically changes itsvolume when charging and discharging the battery, durability againstvolume change may also be improved.

According to an embodiment of the present invention, since a currentcollector includes a first principal plane and a second principal planehaving mutually different roughness between the first principal planeand the second principal plane, occurrence of crack or fracture on theelectrode may be controlled.

Further, according to an embodiment of the present invention, since anegative electrode formed of a current collector includes a firstprincipal plane and a second principal plane having mutually differentroughness between the first principal plane and the second principalplane, occurrence of crack or fracture on the electrode may becontrolled.

According to an embodiment of the present invention, since a batteryincludes a first principal plane and a second principal plane of thenegative current collectors having mutually different roughness betweenthe first principal plane and the second principal plane, highercapacity of the battery may be obtained by forming the battery using thenegative electrode active material that drastically changes its volumewhile controlling occurrence of crack or fracture on the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B respectively show a partially sectioned schematicperspective view and a cross-sectional schematic view illustrating abattery of one embodiment according to an embodiment of the presentinvention.

FIGS. 2A and 2B respectively show a partially sectioned schematicperspective view and a cross-sectional schematic view illustrating abattery of another embodiment according to an embodiment of the presentinvention.

FIGS. 3A to 3C respectively show a partially sectioned schematicperspective view illustrating a battery of still another embodiment anda schematic view illustrating bending bodies in a first and secondembodiments according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings.

It should be noted that the following description includes a currentcollector and a negative electrode according to an embodiment of thepresent invention form a battery according to an embodiment of thepresent invention. However, the current collector and the negativeelectrode according to an embodiment of the present invention are notlimited thereto, and the current collector and the negative electrodeaccording to an embodiment of the present invention may not form abattery.

For example, the current collector and the negative electrode accordingto an embodiment of the present invention may form independent parts.

First Embodiment

A current collector, a negative electrode, and a battery according tofirst embodiment of the present invention will be described below.

An element winding type rectangular battery will be described as shownin FIG. 1A illustrating a partially sectioned schematic perspective viewaccording to an embodiment of the present invention.

As shown in FIG. 1A, a battery 1 according to the embodiment of thepresent invention includes an electrode winding body 3 located around acenter 4 inside a prismatic battery can 2, an upper surface of which isopened and enclosed with a battery lid 5.

The battery can 2 is formed of a nickel-plated iron, and the electrodewinding body 3 includes mutually faced wound positive and negativeelectrodes 9 and 10 through a pair of wound separators 7 and 8containing electrolytes.

The battery lid 5 is attached to the battery can 2 by caulking throughgaskets and the like. Specifically, the inside of the battery can 1 isair-tightly enclosed with the battery can 2 and the battery 5.

FIG. 1B schematically shows a cross-sectional structure of a windingsurface of the winding body according to an embodiment of the presentinvention.

The electrode winding body 3 according to the embodiment of the presentinvention includes strip-shaped (thin plate-shaped) positive andnegative electrodes 9 and 10 that are mutually faced through separators7 and 8 containing electrolytes.

It should be noted that, although FIG. 1B schematically shows that theelectrode winding body 3 forming a rectangular winding, the electrodewinding body 3 has a cross-sectional shape having a curved portion(non-bent curved portion) such as an elliptic form inside the long andnarrow battery can 2.

A positive electrode lead wire (not shown) formed of aluminum (Al) andthe like, and a negative electrode lead wire (not shown) made of nickel(Ni) and the like are respectively connected to the positive andnegative electrodes 9 and 10 of the electrode winding body 3. Thepositive lead wire is welded to a safety valve mechanism 6 toelectrically connect to the battery lid 5. The negative electrode leadwire is directly

For example, in the positive electrode 9 including a positive electrodecurrent collector 11 with a first principal plane 11 a corresponding tothe inner surface and a second principal plane corresponding to theouter surface of the winding structure, an internal positive electrodeactive material layer 12 is formed on the side of the first principalplane 11 a and an external positive electrode active material layer 13is formed on the side of the second principal plane 11 b, respectively.

Both the internal positive electrode active material layer 12 and theexternal positive electrode active material layer 13 may not necessarilybe included. It is preferable that the internal positive electrodeactive material layer 12 and the external positive electrode activematerial layer 13 be selectively provided according to a desiredconfiguration or desired properties of an objective battery. Thepositive electrode current collector 11 may be formed of aluminum,nickel, stainless steel, or the like.

The internal positive electrode active material layer 12 and theexternal positive electrode active material layer 13 contain any one ofor two or more of positive electrode materials that can insert andextract lithium ions as a positive electrode active material and mayoptionally contain a conductive material such as a carbon material and abinder such as poly(vinylidene fluoride). As examples of the lithiumtransition metal composite oxide, a compound shown by a general formulaLixMO2 may preferably given. Since a lithium-containing metal compositeoxide may generate a high voltage and a high energy density; highercapacity for the secondary battery may be realized. For example, Mpreferably represents at least one type of transition metal elementsselected from the group consisting of cobalt, nickel, and manganese(Mn). The subscript x represents the value that may vary with chargingand discharging state of the battery and may fall in the range of0.5≦x≦1.10. The specific examples of lithium transition metal compositeoxide may include LiCoO₂ or LiNiO₂. Notice that the positive electrodeactive material may be used alone or a combination of two or more.

For example, in the negative electrode 10 including a negative electrodecurrent collector 14 with an first principal plane 14 a corresponding tothe inner surface and a second principal plane corresponding to theouter surface of the winding structure, an internal negative electrodeactive material layer 15 is formed on the side of the first principalplane 14 a and an external negative electrode active material layer 16is formed on the side of the second principal plane 14 b, respectively.

Both the internal negative electrode active material layer 15 and theexternal negative electrode active material layer 16 may not necessarilybe included. It is preferable that the internal negative electrodeactive material layer 15 and the external negative electrode activematerial layer 16 be selectively provided according to a desiredthickness or desired materials suitable for surface roughness of thenegative current collector 14 as will be described later.

It should be noted that the negative electrode current collector 14 andthe negative electrode 10 are used as the first embodiment of thecurrent collector and the negative electrode.

The negative electrode current collector 14 may be preferably formed ofcopper (Cu), stainless steel, nickel (Ni), titanium (Ti), tungsten (W),molybdenum (Mo) or aluminum (Al). Of these, the metal elements that mayeasily be alloyed with the inner surface and outer surface negativeelectrode active material layers 15 and 16 are preferable. For example,when the inner and outer surface negative electrode active materiallayers 15 and 16 contain at least one type of the individual elements orcompounds selected from the group consisting of silicon (Si) and tin(Sn), copper (Cu), titanium (Ti), aluminum (Al) or nickel (Ni) may begiven as materials that can easily be alloyed. It should be noted thatthe negative electrode current collector 14 may include a single layeror a plurality of layers. In that case, layers that contact with theinner and outer surface negative electrode active material layers 15 and16 may be formed of metal materials that can easily be alloyed with theinner surface and outer surface negative electrode active materiallayers 15 and 16 and other layers may be formed of other metalmaterials.

In the battery 1 according to an embodiment of the present invention, ifroughness (Ra value) of the first and second principal planes 14 a and14 b of the negative electrode current collector 14 forming the negativeelectrode 10 are mutually different, a battery, though having thecurrent collector 14 at least part of which includes rough surface, mayinclude the negative electrode 10 that are not susceptible to crack orfracture, even when forming a thicker active material layer. Here, theRa value represents parameters of surface roughness according to the JIS(Japanese Industrial Standard) standard and implies an arithmetic meansurface roughness.

If the negative electrode current collector 14 differentiates in thesurface roughness between the first and second principal planes 14 a and14 b, occurrence of crack or fracture on the electrode may be controlledwhen the negative electrode active material layer is formed on bothsurfaces of the inner surface and outer surface negative electrodeactive material layers 15 and 16, or when the negative electrode activematerial layer is formed only on one surface. However, when the negativeelectrode active material layer is formed only on one surface, ahigher-performance battery may particularly be obtained. It should benoted that if the active material layer is formed only on one principalplane of the negative electrode current collector 14, and only thesurface where the active material layer is formed includes roughsurface, excellent characteristics may be obtained; and when the activematerial layer is formed on both principal planes, and both of theprincipal planes include rough surfaces having different degrees ofroughness, excellent characteristics may particularly be obtained.

In the surface roughness of the current collector, the roughness Ra ofthe principal plane having higher roughness may preferably be equal toor greater than 0.2 μm. Accordingly, adhesion may be increased. However,when an extreme roughing treatment is applied, if roughness of bothsurfaces of the negative electrode current collector 14 is decreased toinclude mutually different degrees of roughness, the negative electrodecurrent collector 14 is susceptible to crack or fracture. Therefore, thevalue Ra of the principal plane having higher roughness may preferablybe equal to or less than 3.0 μm.

It should be noted that the optimum value of the roughness Ra and therange thereof are affected by the thickness of the current collector.For example, if a current collector having a thickness of about 5 to 20μm available at present is unused but instead a thicker currentcollector is used, drastic roughness may be suppressed to result in lesscrack or fracture. Therefore, it is preferable that the optimum value ofthe roughness Ra and the range thereof be carefully selected based onthe relationship. However, a battery having an extremely thick currentcollector may not increase capacity of the battery due to an increase inthe volume of the current collector portion. Therefore, in the battery 1according to the embodiment of the present invention, as the currentcollector with which cycle characteristics can be maintained and crackor fracture can be prevented, the current collector having a thicknessof about 5 to 30 μm and having the above described range of the Ra value(roughness) may be preferable.

Further, it is preferable that difference in roughness between bothsurfaces of the first and second principal planes 14 a and 14 b may beequal to or greater than 0.05 μm base on the Ra value. In contrast,although one principal plane includes a desired value in roughness, ifroughness of the other surface may have approximately the same roughnessof one principal plane, improvements of characteristics will be limitedto certain degrees as will be described later.

Further, as will be described later, the battery according to anembodiment of the present invention can achieve an excellent effectparticularly when both of the positive electrode 9 and the negativeelectrode 10 includes the active material layers that have a thicknessgreater than 70 μm for the thickness of either one of the currentcollectors. The electrode having such a thick active material layer mayexhibit a decrease in peel strength and may apply large stress to aninterface that does not support an entire surface of the currentcollector.

Accordingly, the electrode becomes susceptible to crack or fracture whencharging and discharging the battery. It should be noted that thethickness of the active material layer may be defined as one obtained atfull discharge where the remaining battery capacity in the apparatususing the battery reaches zero. That is, this case is different from acase where a battery voltage is set to zero by attaching a fixedresistor to a power supply terminal.

In the battery according to an embodiment of the present invention, ifroughness of the first and second principal planes 14 a and 14 b of thenegative electrode current collector 14 are mutually different, crack orfracture of the electrode, though including a particularly thick activematerial layer, may be lowered or prevented while maintaining adhesionto the interface.

The internal and external negative electrode active material layers 15and 16 may contain at least one kind of individual elements or compoundsselected from the group consisting of metal elements or semimetalelements which can be alloyed with lithium (Li) as a negative electrodeactive material due to obtaining high energy density.

Examples of such metal elements or semimetal elements include palladium(Pd), platinum (Pt), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum(Al), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb),arsenic (As), antimony (Sb) or bismuth (Bi). As examples of thesecompounds, compounds shown by the chemical formula Mas, Mbt may begiven. In the chemical formula, Ma represents at least one kind of metalelements and semimetal elements which can be alloyed with lithium (Li)and Mb represents at least one kind of elements other than Ma. The values indicates s>0 and the value t indicates t≧0, respectively.

Of these metal elements and semimetal elements, individual elements suchas silicon (Si), germanium (Ge), tin (Sn) or lead (Pb), or compoundsincluding the individual elements may be preferable, with individualelements of the silicon (Si) or tin (Sn), or compounds formed of theindividual elements of the silicon (Si) or tin (Sn). Thus, theindividual element and the compound of silicon (Si) or tin (Sn) havelarge ability to insert and extract lithium (Li), and may increaseenergy density of the negative electrode 10 depending on a combinationthereof. It should be noted that the compound of silicon (Si) and tin(Sn) may be crystal or amorphous; however, amorphous or an aggregate ofmicrocrystallite may be preferable. The amorphous or microcrystallitemay include a broad pattern that has half the width of a peak in adiffraction pattern obtained by X-ray diffraction analysis using CuKα ascharacteristic X-rays is 0.5° or more at 2θ and ranges of from 30° to60° at 2θ.

Examples of the compound of silicon (Si) and tin (Sn), include SiB₄,SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi2, CaSi₂, CrSi₂,Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N2O, SiOv (0<v≦2), SnOw (0<w≦2), SnSiO₃, LiSiO or LiSnO.

Some of high capacity active materials that can form the first andsecond negative electrode active material layer 15 and 16 of thenegative electrode 10 may drastically change the volume when the batteryis charged and discharged as described earlier. In particular, if thehigh capacity active material contains silicon (Si) or tin (Sn), whenthe active material layer is thin, the volume may change drastically topeel off the layer from the interface of the current collector and toapply stress to the entire inside of the battery when the battery ischarged and discharged, thereby further causing the electrode to beeither cracked or fractured. In the battery according to the embodimentof the present invention, when the individual element or compound ofsilicon (Si) or tin (Sn) is used as the negative electrode activematerial to obtain high energy density, since the negative electrode cancontrol crack or fracture, thereby forming a large capacity batterywithout the above-mentioned issues.

The first and second negative electrode active material layers 15 and 16may be preferably formed by at least one method selected from the groupconsisting of a vapor-phase method, a liquid-phase method and asintering method. Specifically, the battery may be prevented from beingdestroyed as the internal and external negative electrode activematerial layers 15 and 16 are expanded and contracted when the batteryis charged and discharged and the negative electrode current collector14 and the first and second negative electrode active material layers 15and 16 can be integrated to improve electron conductivity in theinternal and external negative electrode active material layers 15 and16. The binder and gaps may be decreased or eliminated so that thenegative electrode 30 may be reduced in thickness.

It should be noted that the baking method includes mixing powdercontaining active material and the binder to mold a layer, and theresultant layer is heat-treated in the non-oxidizing atmosphere to forma denser layer than the layer before the heat treatment.

The first and second negative electrode active material layers 15 and 16may be preferably formed by at least one method selected from the groupconsisting of a vapor-phase method, a liquid-phase method and asintering method. The internal and external negative electrode activematerial layers 15, 16 may preferably be alloyed with the negativeelectrode current collector 14 at least on a part of the interfacebetween the internal and external negative electrode active materiallayers 15, 16 and the negative electrode current collector 14.Specifically, at the interface, elements of the negative electrodecurrent collector 14 should preferably be diffused into the innersurface and outer surface negative electrode active material layers 15and 16 or elements of the inner surface and outer surface negativeelectrode active material layers 15 and 16 should preferably be diffusedinto the negative electrode current collector 14 or those elementsshould preferably be diffused to each other. Although it is frequentlyobserved that the alloying may take place simultaneously when the innersurface and outer surface negative electrode active material layers 15and 16 are formed by the vapor-phase method, the liquid-phase method orthe sintering method, the alloying may take place due to a further heattreatment. It should be noted that the above-mentioned diffusion ofelements may be included in alloying in the application.

It should be noted that the first and second negative electrode activematerial layers 15 and 16 may be formed by coating, specifically,negative electrode active materials and powder may optionally be bondedwith a binder such as vinylidene polyfluoride.

In this case, powder of silicon (Si) or tin (Sn) compound may preferablyhave a primary particle diameter selected in a range of from 0.1 μm to35 μm and more preferably the above primary particle diameter may beselected in a range of from 0.1 μm to 25 μm. If the particle diameter issmaller than this range, an undesired reaction occurs remarkably betweenthe particle surface and an electrolytic solution, thereby deterioratingcapacity or efficiency of the electrodes. If, on the other hand, theparticle diameter is larger than this range, a reaction between it andlithium (Li) may not proceed within the particle, thereby decreasing thecapacity of the electrodes. It should be noted that as a particle sizemeasuring method, an observation method based on an optical microscopeor electron microscope or laser diffraction method may be given, and itis preferable that the above observation method or the above laserdiffraction method may be selectively used in response to the particlesize region. It is also preferable that classification may be carriedout to obtain a desired particle size. A classification method is notparticularly limited, and a sieve or a wind power classifier may be usedin a dry method or a wet method.

It should be noted that powder of the individual element or compound ofsilicon (Si) or tin (Sn) can be manufactured by a related-art methodused in a powder metallurgy and the like. Examples of the related-artmethod include a method in which a raw material is melted by a meltingfurnace such as an arc smelting furnace and a high-frequency inducedheating furnace, cooled and ground, a method of quenching a melted metalof a raw material such as a single roll quenching method, a twin-rollquenching method, a gas atomizing method, a water atomizing method or acentrifugal atomizing method and a method in which a melted metal of araw material is solidified by a cooling method such as a single rollquenching method and a twin-roll quenching method and ground by asuitable method such as a mechanical alloying method. In particular, itis preferable that the gas atomizing method or the mechanical alloyingmethod may be used. It should be noted that these synthesis and grindingmay preferably be carried out in the inert gas atmosphere such as argon(Ar) gas, nitrogen (N) gas or helium (H) gas or in vacuum atmosphere inorder to prevent metals from being oxidized by oxygen (O) in the air.

The separators 7 and 8 may separate the positive electrode 9 and thenegative electrode 10 from each other and they may pass lithium (Li)ions while preventing an electric current from being short-circuitedwhen both electrodes 9 and 10 contact with each other, and they may beformed of a micro-porous polyolefin film such as a polyethylene film ora polypropylene film, for example. In order to maintain safety, it ispreferable that the separators 7 and 8 may have a function to close themicro-pores by hot-melting at a temperature higher than a predeterminedtemperature (e.g., 120° C.), thereby increasing resistance so that anelectric current may be interrupted. More than two separators mainlymade of polyethylene and more than two separators with differentcompositions mainly made of polypropylene can be bonded.

The separators 7 and 8 are impregnated with an electrolytic solution(not shown). This electrolytic solution may contain a solvent and anelectrolytic salt dissolved into this solvent, and may optionallycontain various kinds of additives.

Examples of the solvents include propylene carbonate, ethylenecarbonate, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxyethane, 1, 2-diethoxy ethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, diethyl ether,sulfolane, methyl sulfolane, acetonitrile, propylnitrile, anisole,acetic ester or propionic acid ester. The additives may be used alone ora combination of tow or more.

Examples of the electrolytic salt include LiClO₄, LiAsF₆, LiPF₆, LiBF₄,LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiN(C₄F₉SO₂)(CF₃SO₂),LiCl or LiBr. Of these electrolytic salts, LiClO₄, LiAsF₆, LiPF₆, LiBF₄,LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ or LiN(C₄F₉SO₂)(CF₃SO₂)should be preferable. Of these electrolytic salts, LiPF₆ or LiBF₄ shouldbe particularly preferable. Any one of the above electrolytic salts maybe used as the above electrolytic salt or more than two kinds ofelectrolytic salts may be mixed and used as the above electrolytic salt.

Second Embodiment

A current collector, a negative electrode and a battery according to asecond embodiment of the present invention will be described.

In this embodiment, a so-called element winding type cylindrical batteryshown in a partly cutaway perspective view of FIG. 2A will be described.

As shown in FIG. 2A, a battery 21 according to the embodiment of thepresent invention includes a cylindrical battery can 22 with its uppersurface opened in which a electrode winding body 23 is located at acenter pin 24 (not shown) and which is sealed by a battery lid 25.

The battery can 22 is configured by a nickel-plated iron, and theelectrode winding body 23 has an arrangement in which a positiveelectrode 29 and a negative electrode 30 similarly wound are located inan opposing fashion through a pair of wound separators 27 and 28containing electrolyte.

The battery lid 25 includes a safety valve mechanism 38 together with aheat sensitive resistance element (positive temperature coefficientwhich will hereinafter be simply referred to as a “PTC element”) 39incorporated therein, and it is attached to the battery can 22 whencaulked through gaskets (not shown) and the like. That is, the inside ofthe battery 21 is hermetically closed by the battery can 22 and thebattery lid 25.

The safety valve mechanism 38 is electrically connected to the batterylid 25 through the PTC element 39. When an internal pressure of thebattery 21 is increased to be higher than a constant value by insideshort-circuiting or with application of heat from the outside, abuilt-in disk plate, for example, is caused to invert to disconnectelectric connection between the battery lid 25 and the electrode windingbody 23. The PTC element 39 may prevent abnormally-intensive heat frombeing generated due to a large electric current by limiting an electriccurrent increased by the increase of resistance when a temperaturerises.

FIG. 2B schematically shows a cross-sectional structure of the windingsurface of the electrode winding body 23 according to the embodiment ofthe present invention.

In this embodiment, the electrode winding body 23 has an arrangement inwhich the strip-like (thin plate-like) positive electrode and negativeelectrodes 29 and 30 are located in an opposing fashion through theseparators 27 and 28 containing electrolyte, these positive and negativeelectrodes 29 and 30 being wound around the electrode winding body 23.

A positive lead wire made of aluminum (Al), for example, and a negativelead wire made of nickel (Ni) and the like (not shown) are respectivelyconnected to the positive electrode 29 and the negative electrode 30 ofthe electrode winding body 23. A positive lead wire is welded to thesafety valve mechanism 38 and thereby electrically connected to thebattery lid 25, and the negative lead wire is directly welded to thebattery can 22 and thereby electrically connected thereto.

Here, the positive electrode 29 includes a positive electrode currentcollector 31 including a first principal plane 31 a used as an innersurface in the winding structure and a second principal plane 31 b usedas an outer surface wherein a first positive electrode active materiallayer 32 is formed on the side of the first principal plane 31 a and asecond positive electrode active material layer 33 is formed on the sideof the second principal plane 31 b.

Both of the first and second positive electrode active material layers32 and 33 need not always be provided and they should preferably beselected and configured in response to target battery arrangement andcharacteristics. The positive electrode current collector 31 may be madeof aluminum (Al), nickel (Ni) or stainless steel, for example.

Also, the first and second positive electrode active material layers 32and 33 may contain a positive electrode active material and they maycontain a conductivity assisting agent such as a carbonaceous materialand a binder such as poly(vinylidene) fluoride if necessary. Lithiumcontaining metal composite oxide expressed by a general formulaLi_(x)MO₂, for example, should preferably be used as the positiveelectrode active material because the lithium containing metal compositeoxide is able to generate a high voltage and it is high in density sothat it can make the secondary battery become higher in capacity. Itshould be noted that M is more than one kind of transition metal and itshould be at least one kind selected from a group consisting of cobalt(Co), nickel (Ni) and manganese (Mn). The x may differ depending on thebattery charging and discharging states and it is a value generallyselected in a range of 0.05≦x≦1.10. LiCoO₂ or LiNiO₂ may be enumeratedas specific examples of such lithium containing metal composite oxide.It should be noted that the positive electrode active material may useany one kind of lithium containing metal composite oxide and that it maymix more than two kinds of lithium containing metal composite oxides.

On the other hand, the negative electrode 30 includes a negativeelectrode current collector 34 having a first principal plane 34 a usedas an inner surface in the winding structure and a second principalplane 34 b used as an outer surface and in which a first negativeelectrode active material layer 35 is formed on the side of the firstprincipal plane 34 a and a second negative electrode active materiallayer 36 is formed on the side of the second principal plane 34 b,respectively.

It should be noted that both of the first and second negative electrodeactive material layers 35 and 36 need not always be provided as will bedescribed later on. Thicknesses and materials thereof should preferablybe selected in response to roughness of the surface of the negativeelectrode current collector 34 which will be described later on.

It should be noted that the negative electrode current collector 34 andthe negative electrode 30 may be used as the current collector and thenegative electrode according to the second embodiment of the presentinvention.

In the battery 31 according to an embodiment of the present invention,if roughness (Ra value) of the first and second principal planes 34 aand 34 b of the negative electrode current collector 34 forming thenegative electrode 30 are mutually different, a battery, though havingthe current collector 34 at least part of which includes rough surface,may include the negative electrode 30 that are not susceptible to crackor fracture, even when forming a thicker active material layer.

Here, the Ra value represents parameters of surface roughness accordingto the JIS (Japanese Industrial Standard) standard and implies anarithmetic mean surface roughness.

If the negative electrode current collector 34 differentiates in thesurface roughness between the first and second principal planes 34 a and34 b, occurrence of crack or fracture on the electrode may be controlledwhen the negative electrode active material layer is formed on bothsurfaces of the inner surface and outer surface negative electrodeactive material layers 35 and 36, or when the negative electrode activematerial layer is formed only on one surface. However, when the negativeelectrode active material layer is formed only on one surface, ahigher-performance battery may particularly be obtained. It should benoted that if the active material layer is formed only on one principalplane of the negative electrode current collector 34, and only thesurface where the active material layer is formed includes roughsurface, excellent characteristics may be obtained; and when the activematerial layer is formed on both principal planes, and both of theprincipal planes include rough surfaces having different degrees ofroughness, excellent characteristics may particularly be obtained.

In the surface roughness of the current collector, the roughness Ra ofthe principal plane having higher roughness may preferably be equal toor greater than 0.2 μm. Accordingly, adhesion may be increased. However,when an extreme roughing treatment is applied, if roughness of bothsurfaces of the negative electrode current collector 14 is decreased toinclude mutually different degrees of roughness, the negative electrodecurrent collector 14 is susceptible to crack or fracture. Therefore, thevalue Ra of the principal plane having higher roughness may preferablybe equal to or less than 3.0 μm.

It should be noted that the optimum value of the roughness Ra and therange thereof are affected by the thickness of the current collector.For example, if a current collector having a thickness of about 5 to 20μm available at present is unused but instead a thicker currentcollector is used, drastic roughness may be suppressed to result in lesscrack or fracture. Therefore, it is preferable that the optimum value ofthe roughness Ra and the range thereof be carefully selected based onthe relationship. However, a battery having an extremely thick currentcollector may not increase capacity of the battery due to an increase inthe volume of the current collector portion. Therefore, in the battery21 according to the embodiment of the present invention, as the currentcollector with which cycle characteristics can be maintained and crackor fracture can be prevented, the current collector having a thicknessof about 5 to 30 μm and having the above described range of the Ra value(roughness) may be preferable.

Further, it is preferable that difference in roughness between bothsurfaces of the first and second principal planes 34 a and 34 b may beequal to or greater than 0.05 μm base on the Ra value. In contrast,although one principal plane includes a desired value in roughness, ifroughness of the other surface may have approximately the same roughnessof one principal plane, improvements of characteristics will be limitedto certain degrees as will be described later.

Further, as will be described later, the battery according to anembodiment of the present invention can achieve an excellent effectparticularly when both of the positive electrode 29 and the negativeelectrode 30 includes the active material layers that have a thicknessgreater than 70 μm for the thickness of either one of the currentcollectors. The electrode having such a thick active material layer mayexhibit a decrease in peel strength and may apply large stress to aninterface that does not support an entire surface of the currentcollector.

Accordingly, the electrode becomes susceptible to crack or fracture whencharging and discharging the battery. It should be noted that thethickness of the active material layer may be defined as one obtained atfull discharge where the remaining battery capacity in the apparatususing the battery reaches zero. That is, this case is different from acase where a battery voltage is set to zero by attaching a fixedresistor to a power supply terminal.

In the battery according to an embodiment of the present invention, ifroughness of the first and second principal planes 34 a and 34 b of thenegative electrode current collector 34 are mutually different, crack orfracture of the electrode, though including a particularly thick activematerial layer, may be lowered or prevented while maintaining adhesionto the interface.

The negative electrode current collector 34 should be preferably made ofcopper (Cu), stainless steel, nickel (Ni), titanium (Ti), tungsten (W),molybdenum (Mo) or aluminum (Al). Of these metal elements, the negativeelectrode current collector 34 should preferably be made of metals whichcan easily be alloyed with the inner surface and outer surface negativeelectrode active material layers 35 and 36. For example, when the innerand outer surface negative electrode active material layers 35 and 36contain at least one kind selected from a group consisting of individualelements or compounds of silicon (Si) and tin (Sn) as will be describedlater on, copper (Cu), titanium (Ti), aluminum (Al) or nickel (Ni) maybe enumerated as materials that can be alloyed easily.

It should be noted that the negative electrode current collector 34 maybe composed of either a single layer or a plurality of layers. In thatcase, layers that contact with the inner and outer surface negativeelectrode active material layers 35 and 36 may be made of metalmaterials that can be alloyed with the inner surface and outer surfacenegative electrode active material layers 35 and 36 and other layers maybe made of other metal materials.

The inner surface and outer surface negative electrode active materiallayers 35 and 36 may contain at least one kind selected from a groupconsisting of individual elements and compounds of metal elements orsemimetal elements which can be alloyed with lithium metal and lithium(Li) as a negative electrode active material because they can generatehigh energy density.

As such metal elements or semimetal elements, there can be enumeratedpalladium (Pd), platinum (Pt), zinc (Zn), cadmium (Cd), mercury (Hg),aluminum (Al), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead(Pb), arsenic (As), antimony (Sb) or bismuth (Bi). Compounds expressedby a chemical formula Ma_(s)Mb_(t), for example, may be enumerated asthese compounds mentioned above. In this chemical formula, Ma expressesat least one kind of metal elements and semimetal elements which can bealloyed with lithium (Li) and Mb expresses at least one kind of otherelements than Ma. The values of s and t are given by inequalities of s>0and t≧0, respectively.

Of these metal elements and semimetal elements, individual elements orcompounds of silicon (Si), germanium (Ge), tin (Sn) or lead (Pb) shouldbe preferable and particularly-preferable metal elements and semimetalelements are individual elements of the silicon (Si) or tin (Sn) orcompounds thereof. The reason for this is that the individual elementand the compound of silicon (Si) or tin (Sn) have large ability toinsert and extract lithium (Li) and that they are able to increaseenergy density of the negative electrode 30 depending on a combinationthereof. It should be noted that the compound of silicon (Si) and tin(Sn) may be either crystal or amorphous and that it should preferably bea polymer of amorphous or microcrystal. The amorphous or microcrystalmay have a pattern in which a half width of a peak of a diffractionpattern obtained by X-ray diffraction analysis using CuKα ascharacteristic X-rays is higher than 0.5° at 2θ and it may also have abroad pattern in which a half width ranges of from 30° to 60° at 2θ.

As the compound of silicon (Si) and tin (Sn), there may be enumeratedSiB₄, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂,CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N₂O, SiO_(v) (0<v≦2), SnO_(w) (0<w≦2), SnSiO₃, LiSiO or LiSnO, forexample.

Some of high capacity active materials that can construct the innersurface and outer surface negative electrode active material layer 35and 36 of the negative electrode 30 may be caused to change its volumevehemently when the battery is charged and discharged as mentionedbefore. In particular, if the high capacity active material containssilicon (Si) or tin (Sn), then even when the active material layer isthin, its volume may change considerably to release the layer from theinterface of the current collector and to apply stress to the whole ofthe inside of the battery when the battery is charged and discharged,which further causes the electrode to be either cracked or split.According to the arrangement of the battery according to the embodimentof the present invention, similarly to the first embodiment, when theindividual element or compound of silicon (Si) or tin (Sn) is used asthe negative electrode active material in order to obtain high energydensity, since it is possible to suppress the negative electrode frombeing either cracked or split, it becomes possible to construct alarge-capacity battery in which the problems can be avoided.

The inner surface and outer surface negative electrode active materiallayers 35 and 36 should be preferably formed by at least one methodselected from a group consisting of a vapor-phase method, a liquid-phasemethod and a sintering method.

Specifically, the reason for this is that this arrangement can suppressthe battery from being destroyed as the inner surface and outer surfacenegative electrode active material layers 35 and 36 are expanded andcontracted when the battery is charged and discharged and that thenegative electrode current collector 34 and the inner surface and outersurface negative electrode active material layers 35 and 36 can beintegrated to improve electronic conductivity in the inner surface andouter surface negative electrode active material layers 35 and 36. Also,the binder and gaps can be decreased or removed so that the negativeelectrode 30 can be reduced in thickness.

The inner surface and outer surface negative electrode active materiallayers 35 and 36 should preferably be alloyed with the negativeelectrode current collector 34 at least on a part of the interfacebetween them and the negative electrode current collector 34.Specifically, at the interface, constitutive elements of the negativeelectrode current collector 34 should preferably be diffused into theinner surface and outer surface negative electrode active materiallayers 35 and 36 or constitutive elements of the inner surface and outersurface negative electrode active material layers 35 and 36 shouldpreferably be diffused into the negative electrode current collector 34or those constitutive elements should preferably be diffused to eachother. Although it is frequently observed that this alloying may takeplace simultaneously when the inner surface and outer surface negativeelectrode active material layers 35 and 36 are formed by the vapor-phasemethod, the liquid-phase method or the sintering method, the alloyingmay take place due to a further heat treatment. It should be noted thatthe above-mentioned diffusion of elements may be included in alloying inthe application of the present invention.

It should be noted that the inner surface and outer surface negativeelectrode active material layers 35 and 36 may be formed by coating, tobe concrete, negative electrode active materials and powders may bebonded by a binder such as polyvinyl alcohol, polyimide, polyamideimideand poly(vinylidene) fluoride, if necessary.

In this case, it is preferable that powder of silicon (Si) or tin (Sn)compound should preferably have a primary particle size selected in arange of from 0.1 μm to 35 μm and it is more preferable that the aboveprimary particle size should be selected in a range of from 0.1 μm to 25μm. If the particle size is smaller than this range, then an undesiredreaction between the particle surface and an electrolytic solution,which will be described later on, becomes remarkable and there is then arisk that capacity or efficiency will be deteriorated. If on the otherhand the particle size is larger than this range, then a reactionbetween it and lithium (Li) becomes difficult to proceed within theparticle and there is then a risk that the capacity will be lowered. Itshould be noted that an observation method based on an opticalmicroscope or electron microscope or laser diffraction method may beenumerated as a particle size measuring method and it is preferable thatthe above observation method or the above laser diffraction methodshould be selectively used in response to the particle size region.Also, it is preferable that classification should be carried out inorder to obtain a desired particle size. A classification method is notlimited in particular, and a sieve or a wind power classifier can beused in a dry method or a wet method.

It should be noted that powder of the individual element or compound ofsilicon (Si) or tin (Sn) can be manufactured by a related-art methodused in a powder metallurgy and the like. As the related-art method,there may be enumerated a method in which a raw material is melted by amelting furnace such as an arc remelting furnace and a high-frequencyinduced heating furnace, cooled and ground, a method of quenching amelted metal of a raw material such as a single roll quenching method, atwin-roll quenching method, a gas atomizing method, a water atomizingmethod or a centrifugal atomizing method and a method in which a meltedmetal of a raw material is solidified by a cooling method such as asingle roll quenching method and a twin-roll quenching method and groundby a suitable method such as a mechanical alloying method. Inparticular, it is preferable that the gas atomizing method or themechanical alloying method should be used. It should be noted that thesesynthesis and grinding should preferably be carried out in the inert gasatmosphere such as argon (Ar) gas, nitrogen (N) gas or helium (H) gas orin the vacuum atmosphere in order to prevent metals from being oxidizedby oxygen (O) in the air.

The separators 27 and 28 may separate the positive electrode 29 and thenegative electrode 30 from each other and they may pass lithium (Li)ions while preventing an electric current from being short-circuitedwhen both electrodes 29 and 30 contact with each other, and they may beformed of a micro-porous polyolefin film such as a polyethylene film ora polypropylene film, for example. In order to maintain safety, it ispreferable that the separators 27 and 28 may have a function to closethe micro-pores by hot-melting at a temperature higher than apredetermined temperature (e.g., 120° C.), thereby to increaseresistance so that an electric current may be interrupted. More than twoseparators mainly made of polyethylene and more than two separators withdifferent compositions mainly made of polypropylene can be bonded.

In this embodiment of the present invention, the separators 27 and 28are impregnated with an electrolytic solution (not shown). Thiselectrolytic solution may contain a solvent and an electrolytic saltdissolved into this solvent, and they may contain various kinds ofadditives, if necessary.

As the solvents, there may be enumerated propylene carbonate, ethylenecarbonate, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxyethane, 1, 2-diethoxy ethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, diethyl ether,sulfolane, methyl sulfolane, acetonitrile, propylnitrile, anisole,acetic ester or propionic acid ester. Any one of the above-mentionedadditives may be used as the above solvent or more than two kinds of theabove-mentioned additives may be mixed and used as the above solvent.

As the electrolytic salt, there may be enumerated LiClO₄, LiAsF₆, LiPF₆,LiBF₄, LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂,LiN(C₄F₉SO₂)(CF₃SO₂), LiCl or LiBr. Of these electrolytic salts, LiClO₄,LiAsF₆, LiPF₆, LiBF₄, LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ orLiN(C₄F₉SO₂)(CF₃SO₂) should be preferable. Of these electrolytic salts,LiPF₆ or LiBF₄ should be particularly preferable. Any one of the aboveelectrolytic salts may be used as the above electrolytic salt or morethan two kinds of electrolytic salts may be mixed and used as the aboveelectrolytic salt.

Third Embodiment

A current collector, a negative electrode and a battery according to athird embodiment of the present invention will be described.

In this embodiment of the present invention, a battery of a typedifferent from that of the first embodiment will be described withreference to an example of a so-called element bending system (stacksystem) rectangular battery shown in a partly cutaway perspective viewof FIG. 3A.

A battery 41 according to the embodiment of the present invention has anarrangement in which a bending body 43 a is located within a prismaticbattery can 42 of which upper surface is opened and the battery can 42is sealed by a battery lid 55.

The battery can 42 is made of a nickel-plated iron, for example, and thebending body 43 a has an arrangement in which positive and negativeelectrodes 29 and 30 bent in a like manner are located in an opposingfashion through a pair of separators 47 and 48 bent containing anelectrolyte. It should be noted that the battery can 42 can be made ofaluminum (Al), stainless steel and the like.

The battery lid 55 is attached to the battery can 42 by caulking throughgaskets and the like. That is, the inside of the battery 41 ishermetically closed by the battery can 42 and the battery lid 55.

In this embodiment of the present invention, the bending bond 43 a hasan arrangement in which strip-like (thin plate-like) positive andnegative electrodes 49 and 50 are located in an opposing fashion throughseparators 47 and 48 containing the electrolyte and these elements 49,50 and 47, 48 are bent, respectively.

It should be noted that the bending body 43 a is formed by repeatingbent curved portions within the long and narrow battery can 42 as shownin FIGS. 3A and 3B.

An positive electrode lead wire made of aluminum (Al), for example, anda negative electrode lead wire made of nickel (Ni), for example, arerespectively connected to the positive electrode 49 and the negativeelectrode 50 of the bending body 43 a although not shown. Morespecifically, respective positive electrode lead wire and negativeelectrode lead wire are connected to several portions of the positiveelectrode 49 and the negative electrode 50 as a stack type structure.

Here, the positive electrode 49 includes a positive electrode currentcollector 51 with a first principal plane 51 a used as the inner surfaceof the winding structure and a second principal plane 51 b used as theouter surface and in which an inner surface positive electrode activematerial layer 52 is formed on the side of the first principal plane 51a and an outer surface positive electrode active material layer 53 isformed on the side of the second principal plane 51 b, respectively.

Both of the inner surface positive electrode active material layer 52and the outer surface positive electrode active material layer 53 neednot always be provided and it is preferable that they should beselectively provided in response to a desired battery arrangement anddesired characteristics. The positive electrode current collector 51 ismade of a suitable material such as aluminum (Al), nickel (Ni) orstainless steel.

The inner surface positive electrode active material layer 52 and theouter surface positive electrode active material layer 53 may contain apositive electrode active material and they may contain a conductiveassisting agent such as a carbonaceous material and a binder such aspoly(vinylidene fluoride) if necessary A lithium containing metalcomposite oxide, expressed by a general formula Li_(x)MO₂, might bepreferable as a positive electrode material because the lithiumcontaining metal composite oxide can generate a high voltage and it ishigh in density so that a secondary battery can become higher incapacity. It should be noted that M is more than one kind of transitionmetal and it may be at least one kind selected from a group consistingof cobalt (Co), nickel (Ni) and manganese (Mn). The subscript x maydiffer depending on the charging and discharging state of the batteryand it may be selected so as to satisfy a condition indicated by0.5≦x≦1.10. LiCoO₂ or LiNiO₂ might be enumerated as specific examples ofsuch lithium containing metal composite oxide. It should be noted thatthe positive electrode active material may contain any one of thelithium containing metal composite oxides or may contain a mixture ofmore than two kinds of the lithium containing metal composite oxides.

On the other hand, the negative electrode 50 includes the negativeelectrode current collector 54 having a first principal plane 54 a usedas an inner surface in the winding structure and a second principalplane 54 b used as an outer surface in which an inner surface positiveelectrode active material layer 55 is formed on the side of the firstprincipal plane 54 and an outer surface positive electrode activematerial layer 56 is formed on the side of the second principal plane 54b, respectively.

It should be noted that, as will be described later on, both of theinner and outer surface negative electrode active material layers 55 and56 need not always be provided. Their thicknesses and materials shouldpreferably be selected in response to roughness of the surface of thenegative electrode current collector 54 which will be described lateron.

It should be noted that the negative electrode current collector 54 andthe negative electrode 50 are used as the third embodiment of thecurrent collector and the negative electrode according to an embodimentof the present invention.

The negative electrode current collector 54 should be preferably made ofcopper (Cu), stainless steel, nickel (Ni), titanium (Ti), tungsten (W),molybdenum (Mo) or aluminum (Al). Of these metal elements, the negativeelectrode current collector 54 should preferably be made of metals whichcan easily be alloyed with the inner surface and outer surface negativeelectrode active material layers 55 and 56. For example, when the innerand outer surface negative electrode active material layers 55 and 56contain at least one kind selected from a group consisting of individualelements or compounds of silicon (Si) and tin (Sn) as will be describedlater on, copper (Cu), titanium (Ti), aluminum (Al) or nickel (Ni) maybe enumerated as materials that can be alloyed easily. It should benoted that the negative electrode current collector 54 may be composedof either a single layer or a plurality of layers. In that case, layersthat contact with the inner and outer surface negative electrode activematerial layers 55 and 56 may be made of metal materials that can bealloyed with the inner surface and outer surface negative electrodeactive material layers 55 and 56 and other layers may be made of othermetal materials.

In the battery 41 according to an embodiment of the present invention,if roughness (Ra value) of the first and second principal planes 54 aand 54 b of the negative electrode current collector 54 forming thenegative electrode 50 are mutually different, a battery, though havingthe current collector 34 at least part of which includes rough surface,may include the negative electrode 50 that are not susceptible to crackor fracture, even when forming a thicker active material layer.

Here, the Ra value represents parameters of surface roughness accordingto the JIS (Japanese Industrial Standard) standard and implies anarithmetic mean surface roughness.

If the negative electrode current collector 54 differentiates in thesurface roughness between the first and second principal planes 54 a and54 b, occurrence of crack or fracture on the electrode may be controlledwhen the negative electrode active material layer is formed on bothsurfaces of the inner surface and outer surface negative electrodeactive material layers 55 and 56, or when the negative electrode activematerial layer is formed only on one surface. However, when the negativeelectrode active material layer is formed only on one surface, ahigher-performance battery may particularly be obtained. It should benoted that if the active material layer is formed only on one principalplane of the negative electrode current collector 54, and only thesurface where the active material layer is formed includes roughsurface, excellent characteristics may be obtained; and when the activematerial layer is formed on both principal planes, and both of theprincipal planes include rough surfaces having different degrees ofroughness, excellent characteristics may particularly be obtained.

In the surface roughness of the current collector, the roughness Ra ofthe principal plane having higher roughness may preferably be equal toor greater than 0.2 μm. Accordingly, adhesion may be increased. However,when an extreme roughing treatment is applied, if roughness of bothsurfaces of the negative electrode current collector 54 is decreased toinclude mutually different degrees of roughness, the negative electrodecurrent collector 54 is susceptible to crack or fracture. Therefore, thevalue Ra of the principal plane having higher roughness may preferablybe equal to or less than 3.0 μm.

It should be noted that the optimum value of the roughness Ra and therange thereof are affected by the thickness of the current collector.For example, if a current collector having a thickness of about 5 to 20μm available at present is unused but instead a thicker currentcollector is used, drastic roughness may be suppressed to result in lesscrack or fracture.

Therefore, it is preferable that the optimum value of the roughness Raand the range thereof be carefully selected based on the relationship.However, a battery having an extremely thick current collector may notincrease capacity of the battery due to an increase in the volume of thecurrent collector portion. Therefore, in the battery 41 according to theembodiment of the present invention, as the current collector with whichcycle characteristics can be maintained and crack or fracture can beprevented, the current collector having a thickness of about 5 to 30 μmand having the above described range of the Ra value (roughness) may bepreferable.

Further, it is preferable that difference in roughness between bothsurfaces of the first and second principal planes 54 a and 54 b may beequal to or greater than 0.05 μm base on the Ra value. In contrast,although one principal plane includes a desired value in roughness, ifroughness of the other surface may have approximately the same roughnessof one principal plane, improvements of characteristics will be limitedto certain degrees as will be described later.

Further, as will be described later, the battery according to anembodiment of the present invention can achieve an excellent effectparticularly when both of the positive electrode 49 and the negativeelectrode 50 includes the active material layers that have a thicknessgreater than 70 μm for the thickness of either one of the currentcollectors. The electrode having such a thick active material layer mayexhibit a decrease in peel strength and may apply large stress to aninterface that does not support an entire surface of the currentcollector.

Accordingly, the electrode becomes susceptible to crack or fracture whencharging and discharging the battery. It should be noted that thethickness of the active material layer may be defined as one obtained atfull discharge where the remaining battery capacity in the apparatususing the battery reaches zero. That is, this case is different from acase where a battery voltage is set to zero by attaching a fixedresistor to a power supply terminal.

In the battery according to an embodiment of the present invention, ifroughness of the first and second principal planes 14 a and 14 b of thenegative electrode current collector 14 are mutually different, crack orfracture of the electrode, though including a particularly thick activematerial layer, may be lowered or prevented while maintaining adhesionto the interface.

The internal and external negative electrode active material layers 55and 66 may contain at least one kind of individual elements or compoundsselected from the group consisting of metal elements or semimetalelements which can be alloyed with lithium (Li) as a negative electrodeactive material due to obtaining high energy density.

Examples of such metal elements or semimetal elements include palladium(Pd), platinum (Pt), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum(Al), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb),arsenic (As), antimony (Sb) or bismuth (Bi). As examples of thesecompounds, compounds shown by the chemical formula Mas, Mbt may begiven. In the chemical formula, Ma represents at least one kind of metalelements and semimetal elements which can be alloyed with lithium (Li)and Mb represents at least one kind of elements other than Ma. The values indicates s>0 and the value t indicates t≧0, respectively.

Of these metal elements and semimetal elements, individual elements suchas silicon (Si), germanium (Ge), tin (Sn) or lead (Pb), or compoundsincluding the individual elements may be preferable, with individualelements of the silicon (Si) or tin (Sn), or compounds formed of theindividual elements of the silicon (Si) or tin (Sn). Thus, theindividual element and the compound of silicon (Si) or tin (Sn) havelarge ability to insert and extract lithium (Li), and may increaseenergy density of the negative electrode 10 depending on a combinationthereof. It should be noted that the compound of silicon (Si) and tin(Sn) may be crystal or amorphous; however, amorphous or an aggregate ofmicrocrystallite may be preferable. The amorphous or microcrystallitemay include a broad pattern that has half the width of a peak in adiffraction pattern obtained by X-ray diffraction analysis using CuKα ascharacteristic X-rays is 0.5° or more at 2θ and ranges of from 30° to60° at 2θ.

Examples of the compound of silicon (Si) and tin (Sn), include SiB₄,SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi2, CaSi₂, CrSi₂,Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N2O, SiOv (0<v≦2), SnOw (0<w≦2), SnSiO₃, LiSiO or LiSnO.

Some of high capacity active materials that can form the first andsecond negative electrode active material layer 55 and 56 of thenegative electrode 50 may drastically change the volume when the batteryis charged and discharged as described earlier. In particular, if thehigh capacity active material contains silicon (Si) or tin (Sn), whenthe active material layer is thin, the volume may change drastically topeel off the layer from the interface of the current collector and toapply stress to the entire inside of the battery when the battery ischarged and discharged, thereby further causing the electrode to beeither cracked or fractured. In the battery according to the embodimentof the present invention, when the individual element or compound ofsilicon (Si) or tin (Sn) is used as the negative electrode activematerial to obtain high energy density, since the negative electrode cancontrol crack or fracture, thereby forming a large capacity batterywithout the above-mentioned issues.

The first and second negative electrode active material layers 55 and 56may be preferably formed by at least one method selected from the groupconsisting of a vapor-phase method, a liquid-phase method and asintering method. Specifically, the battery may be prevented from beingdestroyed as the internal and external negative electrode activematerial layers 55 and 56 are expanded and contracted when the batteryis charged and discharged and the negative electrode current collector54 and the first and second negative electrode active material layers 55and 56 can be integrated to improve electron conductivity in theinternal and external negative electrode active material layers 55 and56. The binder and gaps may be decreased or eliminated so that thenegative electrode 50 may be reduced in thickness.

It should be noted that the baking method includes mixing powdercontaining active material and the binder to mold a layer, and theresultant layer is heat-treated in the non-oxidizing atmosphere to forma denser layer than the layer before the heat treatment.

Also, the inner surface and outer surface negative electrode activematerial layers 55 and 56 should preferably be alloyed with the negativeelectrode current collector 54 at least on a part of the interfacebetween them and the negative electrode current collector 54.Specifically, at the interface, constitutive elements of the negativeelectrode current collector 54 should preferably be diffused into theinner surface and outer surface negative electrode active materiallayers 55 and 56 or constitutive elements of the inner surface and outersurface negative electrode active material layers 55 and 56 shouldpreferably be diffused into the negative electrode current collector 54or those constitutive elements should preferably be diffused to eachother. Although it is frequently observed that this alloying may takeplace simultaneously when the inner surface and outer surface negativeelectrode active material layers 55 and 56 are formed by the vapor-phasemethod, the liquid-phase method or the sintering method, the alloyingmay take place due to a further heat treatment. It should be noted thatthe above-mentioned diffusion of elements may be included in alloying inthe application of the present invention.

The first and second negative electrode active material layers 15 and 16may be preferably formed by at least one method selected from the groupconsisting of a vapor-phase method, a liquid-phase method and asintering method. The internal and external negative electrode activematerial layers 55, 56 may preferably be alloyed with the negativeelectrode current collector 54 at least on a part of the interfacebetween the internal and external negative electrode active materiallayers 55, 56 and the negative electrode current collector 54.

Specifically, at the interface, elements of the negative electrodecurrent collector 54 should preferably be diffused into the innersurface and outer surface negative electrode active material layers 55and 56 or elements of the inner surface and outer surface negativeelectrode active material layers 55 and 56 should preferably be diffusedinto the negative electrode current collector 54 or those elementsshould preferably be diffused to each other. Although it is frequentlyobserved that the alloying may take place simultaneously when the innersurface and outer surface negative electrode active material layers 55and 56 are formed by the vapor-phase method, the liquid-phase method orthe sintering method, the alloying may take place due to a further heattreatment. It should be noted that the above-mentioned diffusion ofelements may be included in alloying in the application.

It should be noted that powder of the individual element or compound ofsilicon (Si) or tin (Sn) can be manufactured by a related-art methodused in a powder metallurgy and the like. As the related-art method,there may be enumerated a method in which a raw material is melted by amelting furnace such as an arc remelting furnace and a high-frequencyinduced heating furnace, cooled and ground, a method of quenching amelted metal of a raw material such as a single roll quenching method, atwin-roll quenching method, a gas atomizing method, a water atomizingmethod or a centrifugal atomizing method and a method in which a meltedmetal of a raw material is solidified by a cooling method such as asingle roll quenching method and a twin-roll quenching method and groundby a suitable method such as a mechanical alloying method. Inparticular, it is preferable that the gas atomizing method or themechanical alloying method should be used. It should be noted that thesesynthesis and grinding should preferably be carried out in the inert gasatmosphere such as argon (Ar) gas, nitrogen (N) gas or helium (H) gas orin the vacuum atmosphere in order to prevent metals from being oxidizedby oxygen (O) in the air.

The separators 47 and 48 may separate the positive electrode 49 and thenegative electrode 50 from each other and they may pass lithium (Li)ions while preventing an electric current from being short-circuitedwhen both electrodes 49 and 50 contact with each other, and they may beformed of a micro-porous polyolefin film such as a polyethylene film ora polypropylene film, for example. In order to maintain safety, it ispreferable that the separators 47 and 48 may have a function to closethe micro-pores by hot-melting at a temperature higher than apredetermined temperature (for example, 120° C.) thereby to increaseresistance so that an electric current may be interrupted. More than twoseparators mainly made of polyethylene and more than two separators withdifferent compositions mainly made of polypropylene can be bonded.

The separators 47 and 48 are impregnated with an electrolytic solution(not shown). This electrolytic solution may contain a solvent and anelectrolytic salt dissolved into this solvent, and they may containvarious kinds of additives, if necessary.

As the solvents, there may be enumerated propylene carbonate, ethylenecarbonate, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxyethane, 1, 2-diethoxy ethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, diethyl ether,sulfolane, methyl sulfolane, acetonitrile, propylnitrile, anisole,acetic ester or propionic acid ester. Any one of the above-mentionedadditives may be used as the above solvent or more than two kinds of theabove-mentioned additives may be mixed and used as the above solvent.

As the electrolytic salt, there may be enumerated LiClO₄, LiAsF₆, LiPF₆,LiBF₄, LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂,LiN(C₄F₉SO₂)(CF₃SO₂), LiCl or LiBr. Of these electrolytic salts, LiClO₄,LiAsF₆, LiPF₆, LiBF₄, LiCH₃SO₃, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ orLiN(C₄F₉SO₂)(CF₃SO₂) should be preferable. Of these electrolytic salts,LiPF₆ or LiBF₄ should be particularly preferable. Any one of the aboveelectrolytic salts may be used as the above electrolytic salt or morethan two kinds of electrolytic salts may be mixed and used as the aboveelectrolytic salt.

EXAMPLES

Results obtained when characteristics of the batteries having thearrangements according to the first and second embodiments of thepresent invention were measured will hereinafter be described in detailwith reference to the drawings as specific examples of the presentinvention. In the following examples, reference numerals and symbolsused in the first to third embodiments of the present invention denoteidentical elements and parts.

Thicknesses of active material layers in the following examples areresults obtained when the thicknesses of the negative electrodes in thecompletely discharged state were measured in actual practice, andthicknesses obtained from film deposition to press-molding are slightlylowered values. Thicknesses of opposing electrodes were adjusted in sucha manner that utilization factor of the negative electrode may reach 90%after the active material layers were formed on the surface of thecurrent collector. Also, in any of the examples, the battery was chargedat a constant current density of 5 mA/cm² until a battery voltagereaches 4.2V and at a constant voltage of 4.2V until a current densityreaches 0.2 mA/cm². Also, the battery was discharged at a constantcurrent density of 5 mA/cm² until a voltage reaches 2.5V.

It should be noted that discharge capacity retention rate in thefollowing explanation is assumed to be a capacity retention rate after100 cycles when an initial discharge capacity was set to 100.

Example 1

In this example, the element winding type square battery described inthe first embodiment was manufactured and used.

In this example, an element winding type square battery was manufacturedas follows.

First, the positive electrode 9 was formed. Specifically, a positiveelectrode mixture was prepared by mixing 91 wt % ofLiNi_(0.8)Co_(0.19)Al_(0.01)O₂ having an average secondary particle sizeof 15 μm, 6 wt % of graphite used as a conductive assisting agent and 3wt % of polyvinylidene fluoride used as a binder. After that, thispositive electrode mixture was dispersed into N-methyl-2-pyrrolidone andthereby formed as positive electrode mixture slurry. Subsequently, thispositive electrode mixture slurry was coated on the aluminum positiveelectrode current collector 11 having a thickness of 20 μm, dried andcompression-molded by a roller press machine and thereby the innersurface positive electrode active material layer 12 and the outersurface positive electrode active material layer 13 are formed,resulting in the positive electrode 9 being obtained.

Subsequently, the negative electrode 10 was manufactured. Specifically,first, 12 μm-thick rolled copper foil was prepared, copper particleswere deposited on the surface, one surface or both surfaces withroughness of Ra of 0.05 μm by an electrolytic deposition method andthereby copper foil with a predetermined surface roughness was obtainedas the negative electrode current collector 14. The electrolyticdeposition method in the manufacturing of this negative electrodecurrent collector 14 was carried out by adjusting a time andelectrolytic conditions in the deposition of the copper particles insuch a manner that the first principal plane 14 a used as the innersurface of the winding structure finally and the second principal plane14 b used as the outer surface may have different roughness. Withrespect to the first principal plane 14 a and the second principal plane14 b having predetermined different surface roughness, a mixture ofnatural graphite with a particle size of 25 μm and PVdF at a mixingratio of 95:5 (wt %) was dispersed into NMP. After the negativeelectrode active material layers 15 and 16 was formed by coating theresultant mixture on the negative electrode current collector 14, theywere dried and pressed and thereby the negative electrode 10 wasobtained. It should be noted that the thickness of the active materiallayers was obtained when the thickness of the negative electrode in thecompletely discharged state was measured in actual practice. Thethickness obtained immediately after the electrode was manufactured(from film deposition to press-molding) becomes a little smaller value.

It should be noted that, when the cross section of the negativeelectrode 10 was sliced by a focused ion beam (FIB: Focused Ion Beam) inorder to observe the interface between the negative electrode activematerial layers 15 and 16 and the negative electrode current collector14 and analyzed by AES (Auger electron spectroscopy), it was confirmedthat the negative electrode active material layers 15 and 16 and thenegative electrode current collector 14 were alloyed.

After the positive electrode 9 and the negative electrode 10 weremanufactured, a positive lead wire with an insulating tape attachedthereto was connected to one end of the positive electrode currentcollector 11 of the positive electrode 9, the positive electrode 9 andthe negative electrode 10 were laminated through the 30 μm-thickseparators 7 and 8 made of micro-porous polyethylene film, wound andthereby the electrode winding body 3 with a shortest diameter S of 17.37mm and a longest diameter L of 17.45 mm was manufactured. After theelectrode winding body 3 was formed, both end portions perpendicular tothe winding surface of the electrode winding body 3 were sandwiched by apair of insulating plates, the positive electrode lead wire was weldedto the safety valve mechanism 6, the negative electrode lead wire (notshown) was welded to the bottom portion of the battery can 2 and theelectrode winding body 3 was housed within the battery can 2 made ofiron.

Thereafter, an electrolytic solution was injected into the inside of thebattery can 2. As the electrolytic solution, there was employed suchelectrolytic solution in which LiPF₆ with a concentration of 1 mol/dm³was dissolved into a mixture of ethylene carbonate (EC) used as asolvent and diethyl carbonate (DEC) with a weight ratio of EC:DEC=3:7.

After the electrolytic solution was injected into the inside of thebattery can 2, the battery lid 5 was caulked to the battery can 2through the gasket and thereby the battery 1 was obtained as a squaresecondary battery.

With respect to such battery, batteries corresponding to examples 1-1 to1-7 and comparative examples 1-1 to 1-8 were manufactured by changingcombinations of roughness of the first principal plane 14 a used as theinner surface of the winding structure and the second principal plane 14b used as the outer surface of the winding structure, the thickness ofthe inner surface negative electrode active material layer 15 formed onthe first principal plane 14 a and the thickness of the outer surfacenegative electrode active material layer 16 formed on the secondprincipal plane 14 b, respectively and discharge capacity retentionrates thereof were measured. Measured results are shown on the followingTABLE 1.

TABLE 1 First First principal plane Second Second principal PlanePrincipal active material layer Principal active material layerDischarge Plane Film Plane Film capacity Roughness Thickness RoughnessThickness retention Number Of (μm) Material (μm) (μm) material (μm) rate(%) cracks Example 1-1 0.1 Graphite 60 0.05 Graphite 60 90 0 Example 1-20.2 Graphite 60 0.05 Graphite 60 92 0 Example 1-3 0.4 Graphite 60 0.05Graphite 60 93 0 Example 1-4 0.6 Graphite 60 0.05 Graphite 60 92 0Example 1-5 0.4 Graphite 80 0.05 Graphite 80 90 0 Example 1-6 0.4Graphite 110 0.05 Graphite 110 84 2 Example 1-7 0.4 Graphite 130 0.05Graphite 130 82 3 Comparative 0.05 Graphite 60 0.05 Graphite 60 89 0Example 1-1 Comparative 0.4 Graphite 60 0.4 Graphite 60 88 3 Example 1-2Comparative 0.05 Graphite 80 0.05 Graphite 80 82 0 Example 1-3Comparative 0.4 Graphite 80 0.4 Graphite 80 84 5 Example 1-4 Comparative0.05 Graphite 110 0.05 Graphite 110 77 2 Example 1-5 Comparative 0.4Graphite 110 0.4 Graphite 110 48 9 Example 1-6 Comparative 0.05 Graphite130 0.05 Graphite 130 52 4 Example 1-7 Comparative 0.4 Graphite 130 0.4Graphite 130 33 12 Example 1-8

From the results in the TABLE 1, it could be confirmed that, when thethicknesses of the active material layers 15 and 16 formed on the firstand second principal planes 14 a and 14 b are equal to each other, thebatteries having the arrangements according to an embodiment of thepresent invention in which roughness of the first and second principalplanes 14 a and 14 b is different according to the examples 1-1 to 1-7could exhibit higher discharge retention ratios.

Also, the batteries having the arrangements according to an embodimentof the present invention in the examples 1-1 to 1-7 had lesser cracksand cracks are not produced in, particularly, the batteries of theexamples 1-1 to 1-5. Further, it could be confirmed that the battery ofthe example 1-7 had far excellent characteristics of both cracks anddischarge capacity retention rates as compared with batteries of thecorresponding comparative examples 1-7 and 1-8.

Example 2

In this example, the element winding type square battery explained inthe first example was manufactured and used.

It should be noted that, when the battery was manufactured, an activematerial layer similar to that of the first example was formed so as tohave a thickness of about 110 μm.

In such battery, with respect to combinations of roughness of the firstprincipal plane 14 a used as the inner surface of the winding structureand the second principal plane 14 b used as the winding structure of thenegative electrode current collector 14 constructing the negativeelectrode 10, principal planes with higher roughness were made differentand batteries corresponding to example 2-1 and comparative examples 2-1to 2-3 were manufactured. Then, discharge capacity retention ratesthereof were measured. Measured results are shown on the following TABLE2].

TABLE 2 First First principal plane Second Second principal planeprincipal active material layer principal active material layerDischarge plane Film plane Film capacity roughness thickness roughnessthickness retention Number of (μm) material (μm) (μm) material (μm) rate(%) cracks Example 2-1 0.4 Graphite 110 0.05 — — 90 2 Comparative 0.05Graphite 110 0.05 — — 81 2 example 2-1 Comparative 0.05 Graphite 110 0.4— — 72 6 example 2-2 Comparative 0.4 Graphite 110 0.4 — — 69 8 example2-3

From the results shown in the TABLE 2, it could be confirmed that, whenroughness of the first and second principal planes 14 a and 14 b weremade different, if roughness of the first principal plane 14 a was madehigher than that of the second principal plane 14 b, particularly highdischarge capacity retention rates were exhibited.

Also, with respect to the number of cracks, it could be confirmed fromthe result of the example 2-1 having the arrangement according to anembodiment of the present invention that the example 2-1 can suppressthe number of cracks to the number of cracks equal to or less than thoseof the comparative examples 2-1 to 2-3.

Example 3

In this example, the element winding type square battery described inthe first embodiment was manufactured and used.

It should be noted that, when the battery according to this example wasmanufactured, first, the natural graphite, silicon particles with anaverage particle size of 3 μm and polyamide acid were mixed in the NMPand thereby formed as slurry and this slurry was coated on a currentcollector. Next, after the electrode was dried and press-molded, aresultant molded product was heat-treated at 400° C. for three hours inthe atmosphere of argon (Ar) gas. In that case, a mixing ratio ofpolyamide acid relative to the silicon particles was adjusted so as toreach 10% in weight ratio.

With respect to such battery, while combinations of roughness of thefirst principal plane 14 a used as the inner surface of the windingstructure and the second principal plane 14 b used as the outer surfaceof the winding structure of the negative electrode current collector 14constructing the negative electrode 10, compositions a composition ofthe inner surface negative electrode active material layer 15 formed onthe first principal plane 14 a and a composition of the outer surfacenegative electrode active material layer 16 formed on the secondprincipal plane 16 were respectively being changed, batteriescorresponding to examples 3-1 to 3-4 and comparative examples 3-1 to 3-8were manufactured and discharge capacity retention rates thereof weremeasured. Measured results are shown on the following TABLE 3]. TheTABLE 3 is formed of TABLES 3A and 3B so as to permit a use of asuitably large-scale.

TABLE 3A First First principal plane Second principal Active materiallayer principal plane Film Plane Roughness thickness Roughness (μm)Material (μm) (μm) Example 3-1 0.4 Graphite 110 0.05 Example 3-2 0.4Graphite:Si = 8:2 110 0.05 Example 3-3 0.4 Graphite:Si = 6:4 110 0.05Example 3-4 0.4 Graphite:Si = 3:7 110 0.05 Comparative 0.05 Graphite 1100.05 Example 3-1 Comparative 0.4 Graphite 110 0.4 Example 3-2Comparative 0.05 Graphite:Si = 8:2 110 0.05 Example 3-3 Comparative 0.4Graphite:Si = 8:2 110 0.4 Example 3-4 Comparative 0.05 Graphite:Si = 6:4110 0.05 Example 3-5 Comparative 0.4 Graphite:Si = 6:4 110 0.4 Example3-6 Comparative 0.05 Graphite:Si = 3:7 110 0.05 Example 3-7 Comparative0.4 Graphite:Si = 3:7 110 0.4 Example 3-8

TABLE 3B Second principal plane Active material layer Film Dischargethick- Volume capacity Num- ness changing retention ber of material (μm)rate (%) rate (%) cracks Example 3-1 Graphite 110 1 81 1 Example 3-2Graphite:Si = 8:2 110 10 82 2 Example 3-3 Graphite:Si = 6:4 110 30 79 3Example 3-4 Graphite:Si = 3:7 110 80 72 4 Comparative Graphite 110 1 762 Example 3-1 Comparative Graphite 110 1 52 7 Example 3-2 ComparativeGraphite:Si = 8:2 110 10 69 3 Example 3-3 Comparative Graphite:Si = 8:2110 10 40 11 Example 3-4 Comparative Graphite:Si = 6:4 110 30 60 5Example 3-5 Comparative Graphite:Si = 6:4 110 30 32 15 example 3-6Comparative Graphite:Si = 3:7 110 80 42 4 example 3-7 ComparativeGraphite:Si = 3:7 110 80 12 19 example 3-8

From the results shown in the TABLE 3, it could be confirmed that, whenthe volume change rate of the outer negative electrode active materiallayers 16 formed on the second principal plane 14 b are equal, thebatteries in the examples 3-1 to 3-4 in which the first and secondprincipal planes 14 a and 14 b have different roughness can exhibithigher discharge capacity retention rates.

A difference between the discharge capacity retention rates of theexamples and the comparative examples is increased as the content ofsilicon that can make large-capacity become possible is increased. Also,since the batteries having the arrangement according to an embodiment ofthe present invention in the examples 3-1 to 3-4 have lesser cracks,excellent characteristics with respect to the arrangement of the presentinvention could be confirmed in both of the number of cracks and thedischarge capacity retention rate.

Example 4

In this example, the element winding type square battery described inthe first embodiment was manufactured and used.

It should be noted that, when the battery is manufactured, unlike thefirst embodiment, tin (Sn) having a thickness of about 4 μm was platedon both surfaces of the first and second principal planes 14 a and 14 bof the negative electrode current collector 14 on which cobalt having athickness of about 2 μm was deposited by a vacuum deposition method.Then, a product was heat-treated at 200° C. for six hours in theatmosphere of argon (Ar) gas and thereby the negative electrode 10 wasformed.

With respect to such battery, while combinations of roughness of thefirst principal plane 14 a used as the inner surface of the windingstructure and the second principal plane 14 b used as the outer surfacein the winding structure were being changed and the volume change ratioof the outer surface negative electrode active material layer 16 formedon the second principal plane 14 b was being made constant, batteriescorresponding to the examples 4-1 to 4-4 and the comparative examples4-1 and 4-2 were manufactured and discharge capacity retention ratesthereof were measured. Measured results are shown on the following TABLE4]. The TABLE 4 is formed of TABLES 4A and 4B so as to permit a use ofsuitably large-scale.

TABLE 4A First First principal plane Second principal Active materiallayer principal Plane Film Plane Active Roughness Thickness material(μm) Material (μm) Layer Example 4-1 0.4 Sn + Co 4 + 2 0.05 Example 4-20.4 Sn + Co 4 + 2 0.2 Example 4-3 0.6 Sn + Co 4 + 2 0.2 Example 4-4 0.6Sn + Co 4 + 2 0.5 Comparative 0.05 Sn + Co 4 + 2 0.05 Example 4-1Comparative 0.4 Sn + Co 4 + 2 0.4 Example 4-2

TABLE 4B Second principal plane Active material layer Film DischargeThick- Volume Capacity Num- ness Change Retention ber of material (μm)rate (%) Rate (%) Cracks Example 4-1 Sn + Co 4 + 2 60 72 0 Example 4-2Sn + Co 4 + 2 60 80 1 Example 4-3 Sn + Co 4 + 2 60 78 4 Example 4-4 Sn +Co 4 + 2 60 73 5 Comparative Sn + Co 4 + 2 60 49 0 Example 4-1Comparative Sn + Co 4 + 2 60 44 11 Example 4-2

From the results in the TABLE 4, it could be confirmed that, also whenthe active material layer is made of tin (Sn), the batteries in theexamples 4-1 to 4-4 in which the first and second principal planes 14 aand 14 b are different in roughness according to the arrangement of thepresent invention can exhibit higher discharge capacity retention rates.

Further, the batteries in the examples 4-1 to 4-4 having the arrangementaccording to an embodiment of the present invention have fewer cracksand the number of cracks can further be decreased as a difference ofroughness between the first and second principal planes 14 a and 14 b isincreased.

Example 5

In this example, the element winding type square battery explained inthe first embodiment, the element winding type cylindrical (tubular)battery explained the second embodiment and a stack type square batterywere manufactured and used.

In this example, the element winding type square battery wasmanufactured by a procedure similar to that of the first example.

However, the inner surface negative electrode active material layer 15and the outer surface negative electrode active material layer 16 of thenegative electrode current collector 14 were formed by forming silicon(Si) having a thickness of about 4 μm on the negative electrode currentcollector 14 by an RF (radio frequency) sputtering method. Thereafter, aresultant product was heat-treated at 280° C. for six hours in theatmosphere of argon (Ar) gas and the resultant product was used as anegative electrode.

Also, in this example, the element winding type cylindrical batteryexplained in the second embodiment was manufactured and used.

The element winding type cylindrical battery 21 was manufactured by thefollowing procedure.

First, the positive electrode 29 was manufactured. Specifically, apositive electrode mixture was prepared by mixing 91 wt % ofLiNi_(0.8)Co_(0.19)Al_(0.01)O₂ having an average secondary particle sizeof 15 μm, 6 wt % of graphite used as a conductive assisting agent and 3wt % of poly(vinylidene) fluoride used as a binder. After that, thispositive electrode mixture was dispersed into N-methyl-2-pyrrolidone andthereby formed as positive electrode mixture slurry.

Subsequently, this positive electrode mixture slurry was coated on thealuminum positive electrode current collector 31 having a thickness of20 μm, dried and compression-molded by a roller press machine andthereby the inner surface positive electrode active material layer 32and the outer surface positive electrode active material layer 33 wereformed, resulting in the positive electrode 29 being obtained.

Subsequently, the negative electrode 30 was manufactured. Specifically,first, a 12 μm-thick rolled copper foil was prepared, copper particleswere deposited on the surface, one surface or both surfaces withroughness of Ra of 0.05 μm by an electrolytic deposition method andthereby copper foil with a predetermined surface roughness was obtainedas the negative electrode current collector 34. The electrolyticdeposition method in the manufacturing of this negative electrodecurrent collector 34 was carried out by adjusting a time andelectrolytic conditions in the deposition of the copper particles insuch a manner that the first principal plane 34 a used as the innersurface of the winding structure finally and the second principal plane34 b used as the outer surface may have different roughness. Silicon(Si) having a thickness of about 4 μm was deposited on the firstprincipal plane 34 a and the second principal plane 34 b havingpredetermined different surface roughness of the thus obtained negativeelectrode current collector 34 by an RF sputtering method. Thereafter,the resultant product was heat-treated at 280° C. for six hours in theatmosphere of argon (Ar) gas and the finally obtained product was usedas the negative electrode.

It should be noted that, when the cross section of the negativeelectrode 30 was sectioned by a focused ion beam (FIB: Focused Ion Beam)in order to observe the interface between the negative electrode activematerial layers 35 and 36 and the negative electrode current collector34 and analyzed by AES (Auger electron spectroscopy), it was confirmedthat the negative electrode active material layers 35 and 36 and thenegative electrode current collector 34 were alloyed.

After the positive electrode 29 and the negative electrode 30 weremanufactured, a positive lead wire with an insulating tape attachedthereto was connected to one end of the positive electrode currentcollector 31 of the positive electrode 29, the positive electrode 29 andthe negative electrode 30 were laminated through the 30 μm-thickseparators 27 and 28 made of a micro-porous polyethylene film, wound andthereby the electrode winding body 23 having a shortest diameter S of17.37 mm and a longest diameter L of 17.45 mm was manufactured. Afterthe electrode winding body 23 was formed, both end portionsperpendicular to the winding surface of the electrode winding body 23were sandwiched by a pair of insulating plates, the positive electrodelead wire was welded to the safety valve mechanism 36, the negativeelectrode lead wire (not shown) was welded to the bottom portion of thebattery can 22 and the electrode winding body 23 was housed within thebattery can 22 made of iron.

Thereafter, the center pin 24 was inserted into the center of theelectrode winding body 23. Subsequently, an electrolytic solution wasinjected into the inside of the battery can 22. As the electrolyticsolution, there was employed such electrolytic solution in which LiPF₆with a concentration of 1 mol/dm³ was dissolved into a mixture ofethylene carbonate (EC) used as a solvent and diethyl carbonate (DEC)with a weight ratio of EC:DEC=3:7.

After the electrolytic solution was injected into the inside of thebattery can 22, the battery lid 25 was caulked to the battery can 22through the gasket and thereby the battery 21 having a diameter of 18 mmand a height of 65 mm was obtained as the cylindrical type secondarybattery.

Also, in this example, the element stack type square battery explainedin the third embodiment was manufactured.

The element stack type square battery 41 was manufactured by thefollowing procedure.

First, silicon having a thickness of about 4 μm was deposited on thenegative electrode current collector 54 having a thickness of 20 μm inwhich the first and second principal planes 54 a and 54 b havepredetermined Ra values by an RF sputtering method and the resultantproduct was heat-treated at 280° C. for six hours in the atmosphere ofargon (Ar) gas. Then, the finally obtained product was used as thenegative electrode. Thereafter, the lead wire 46 was attached to thenegative electrode.

On the other hand, cobaltic acid lithium (LiCoO₂) used as a positiveelectrode active material, carbon black used as a conductive materialand poly(vinylidene) fluoride were mixed. N-methyl-2-pyrrolidone used asa dispersion medium was mixed to the above mixture, coated and dried onthe positive electrode current collector 51 made of aluminum foils andthereby the positive electrode active material layers 52 and 53 wereformed on the first and second principal planes 51 a and 51 b of thepositive electrode current collector 51. Thereafter, the lead wire 45was attached.

Subsequently, the thus manufactured negative electrode 50 and positiveelectrode 49 were wound through the separators 47 and 48 made of themicro-porous polyethylene film and sandwiched between the exteriormembers 42 and 44 made of aluminum laminated film. Then, an electrolyticsolution was injected into the inside of the exterior members 42 and 44,the exterior members 42 and 44 were hermetically closed and thereby thebattery 41 in which the electrode winding body 43 was provided withinthe hermetically sealed structure was manufactured.

With respect to such battery, while the combinations of roughness of thefirst principal plane used as the inner surface of the winding structureand the second principal plane used as the outer surface in the windingstructure, thicknesses of the inner surface negative electrode activematerial layer formed on the first principal plane and thicknesses ofthe outer surface negative electrode active material layer formed on thesecond principal plane were being respectively changed, batteriescorresponding to the examples 5-1 to 5-3 and the comparative examples5-1 to 5-6 were manufactured and discharge capacity retention ratesthereof were measured. Measured results are shown on the following TABLE5]. The TABLE 5 is formed of TABLES 5A and 5B so as to permit a use of asuitably large-scale.

TABLE 5A First First principal plane Second principal Active materiallayer principal Plane Film Plane Roughness Thickness Roughness (μm)Material (μm) (μm) Example 5-1 0.5 Si 4 0.2 Example 5-2 0.5 Si 4 0.2Example 5-3 0.5 Si 4 0.2 Comparative 0.2 Si 4 0.2 example 5-1Comparative 0.5 Si 4 0.5 Example 5-2 Comparative 0.2 Si 4 0.2 Example5-3 Comparative 0.5 Si 4 0.5 example 5-4 Comparative 0.2 Si 4 0.2Example 5-5 Comparative 0.5 Si 4 0.5 Example 5-6

TABLE 5B Second principal plane Active material layer Film DischargeThick- Volume Capacity Num- ness Change Retention ber of material (μm)rate (%) Rate (%) Crack Example 5-1 Si 4 Stack 69 0 (square type)Example 5-2 Si 4 Winding 80 2 (square type) Example 5-3 Si 4 Winding 822 (square type) Comparative Si 4 Winding 62 0 Example 5-1 (square type)Comparative Si 4 Stack 43 1 Example 5-2 (square type) Comparative Si 4Stack 72 1 Example 5-3 (square type) Comparative Winding Example 5-4 Si4 (square type) 73 5 Comparative Si 4 Winding 61 3 Example 5-5 (squaretype) Comparative Si 4 Winding 55 11 Example 5-6 (square type)

From the results on the TABLE 5, the examples 5-1 to 5-3 in which thefirst and second principal planes are different in roughness accordingto the arrangements of the present invention in any types of thebatteries can exhibit higher discharge capacity retention rates and thenumber of cracks can be decreased. Therefore, it could be confirmed thatfar excellent characteristics can be obtained in both of the number ofcracks and the discharge capacity retention rate.

As described in the above-mentioned embodiments and examples, accordingto the battery of the present invention, since roughness of one side ofthe current collector is increased, roughness of one side is decreasedrelatively and the surface roughness values of the front and backsurfaces are changed, it is possible to avoid the electrode from beingeither split or cracked when the battery is charged and discharged. As aresult, it becomes possible to maintain high cycle characteristics evenin the large-capacity battery.

More specifically, according to an embodiment of the present invention,it is possible to obtain a battery in which the negative electrode isformed of the active material layer of which volume is changedconsiderably and which includes such negative electrode while theelectrode can be suppressed from being either cracked or split. On theother hand, there is a battery with a specification which is easy tocrack or split depending on the thickness of the current collector andother arrangement of the battery. In that case, it is also possible toobtain an optimum battery arrangement by using suitable arrangementssuch as to keep roughness of one side at high level, to keep roughnessof the other side at low level, to locate the thick active materiallayer at the surface with high roughness and to locate the thin activematerial layer at the surface with low roughness. It should be notedthat, as mentioned before, particularly large improvements ofcharacteristics could be confirmed in the winding type elementarrangement battery to which local stress of electrode can be easilyapplied.

It should be noted that the materials available in the above-describedembodiments and numerical value conditions such as their quantities,their treatment times and their dimensions are merely those of thesuitable examples and also dimensions, shapes and placementrelationships in the respective sheets of drawings are describedschematically. That is, the present invention is not limited to thoseembodiments.

For example, the present invention can be applied to various batteryarrangements and the containers thereof such as the exterior member andthe battery can are not limited to the ones. Therefore, the presentinvention can be modified and changed variously.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A battery comprising: a positive electrode, and anegative electrode, wherein, the positive electrode and the negativeelectrode are spirally wound to form a wound body, the negativeelectrode comprises (1) an active material layer having an activematerial selected from at least one of Si or Sn, and (2) a negativeelectrode current collector having (a) a first principal plane facingoutward and corresponding to an outer face of the wound body and (b) asecond principal plane facing inward and corresponding to an inner faceof the wound body, and a difference between a first surface roughness ofthe first principal plane of the negative current collector and a secondsurface roughness of the second principal plane of the negative currentcollector is greater than 0.05 μm.
 2. A battery according to claim 1,wherein a surface roughness of the first principal plane of the negativecurrent collector is higher than the a surface roughness of the secondprincipal plane of the negative current collector.
 3. A batteryaccording to claim 1, wherein the first surface roughness is in a rangeof 0.2 μm to 3.0 μm, both inclusive.
 4. A battery according to claim 1,wherein at least one of the active material layer on the first principalplane of the negative current collector or the active material layer onthe second principal plane of the negative current collector has athickness of 70 μm or more at full discharge.
 5. A battery according toclaim 1, wherein the negative current collector has a thickness in therange of 5 μm to 30 μm, both inclusive.
 6. A battery according to claim1, wherein the active material layer of the negative electrode comprisesa graphite material.
 7. A battery according to claim 1, wherein thepositive electrode comprises a lithium transition metal composite oxideincluding a metal element selected from the group consisting of cobalt,nickel, and manganese.
 8. A battery according to claim 1, wherein theactive material layer of the negative electrode has a peak in adiffraction pattern obtained by X-ray diffraction analysis using CuKα of30° to 60°, and half the width of the peak is 0.5° or more at 2θ.
 9. Abattery according to claim 1, wherein the active material has particleswith diameters in the range of 0.1 μm to 25 μm, both inclusive.
 10. Abattery according to claim 1 further comprises an electrolyte comprisingone or more of propylene carbonate, ethylene carbonate, diethylcarbonate, methyl ethyl carbonate, 1,2-dimethoxy ethane, 1,2-diethoxyethane, .gamma.-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether,sulfolane, methyl sulfolane, acetonitrile, propylnitrile, anisole,acetic ester, or propionic acid ester.
 11. A battery according to claim1 further comprises an electrolyte salt, wherein the electrolyte saltcomprises at least one of LiPF₆ or LiBF₄.
 12. An electronic apparatuscomprising the battery according to claim
 1. 13. A negative electrodespirally wound to form a wound body and comprising: an active materiallayer having an active material with at least one of Si or Sn, and anegative electrode current collector having (a) a first principal planefacing outward and corresponding to an outer face of the wound body and(b) a second principal plane facing inward and corresponding to an innerface of the wound body, wherein a difference between a first surfaceroughness of the first principal plane of the negative current collectorand a second surface roughness of the second principal plane of thenegative current collector is greater than 0.05 μm.